Printing plate manufacture



Patented July 14, 1942 UNITED STATES PATENT OFFICE PRINTING PLATE MANUFACTURE No Drawing. Application March 29, 1940, Serial No. 326,725

4 Claims. (Cl. 10'1395) In printing plants, the customary stereotyping process, while covering the advantages of rapidity and flexibility of performance, has a serious disadvantage of limiting pictorial productions to relatively coarse screen character, and it I is impossible to provide illustrations carrying fine detail such as would be desirable in many instances. Furthermore, even when employing the coarser screens, the impression is often not -s sharp and distinct as may be desired. In some newspaper plants there is an effort to meet this difiiculty by etching any matter desired on a thin zinc plate which for the operation of printing is backed up by a steel plate, the assemblage being held together by screws or clamping means. Such a printing element however, while permitting more detail, does not permit routing out of non-printing areas, and does not make possible printing in colors; and furthermore, plates of this kind being made up as they are by bending the zinc plate to conform to the arcuately preformed steel backing plate which is finished to contour to fit the printing cylinder, involve differential stresses in the components of the assembled plate, and if put in high speed heavy duty operation the diiferential stresses tend to occasion creeping between the plates and breakage where the zinc is bent for fastening. In accordance with the present invention, it now becomes possible to provide quickly and conveniently a printing surface with such fine line screen character as may be desired, which will ensure sharp and distinct impressions generally, which can be used in color work, and which moreover is free from disruptive internal stresses involved in production.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described, and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative however, of but a few of the various ways in which the principle of the invention may be employed.

The printing surface is prepared by etching a relatively thin metal sheet, the thickness being such that the sheet is flexible or bendable to the arcuate contour requisite for fitting on a printing cylinder, and dependingupon the size and the character of the design of the cylinder the sheet may be of a size for a substantially complete cylinder or arcuate portion, as appropriate in any instance. The sheet metal of such light gauge stock, for example twenty-five to thirty than the prepared facing plate.

thousandths of an inch, or slightly variant therefrom according to the circumstances, is prepared for etching, and is etched in the subject matter to be reproduced, this involving the cleaning of the sheet, the applying of a dichromated gelatin coating or cold top enamel or resist, and exposing, and developing for instance as in usual or preferred manner, and etching, such as by dilute nitric acid or other acid etch as may be preferred. The metal of the sheet for etching'may be conveniently zinc, or in some instances other metal as applicable to etching, copper, light metal alloys, etc. The sheet, before or after the etching preparation of its printing surface, for instance after, is cleaned on the back and is fiuxed, and is bent to arcuate or cylindrical form corresponding to its contour for the printing cylinder in operation. While other means may be employed to bend and hold the metal plate in position for joining the metal backing the following method is preferred. By the use of a flexible or relatively thin plate, this shaping may be accomplished by a vacuum, the sheet being positioned within a closeable cylindrical or arouate casing providing outer supporting surface of a desired form, and having vacuum ports by which a vacuum is applied to the outer or printing surface of the etched metal sheet. Then, joining metal is united, molten, with the positioned facing sheet, the molten metal being charged in against the back of the prepared printing layer, a suitable central core limiting the thickness of the added metal, the layer of backing metal being generally preferably thicker Thus, for instance, an illustrative thickness for a plate to be used in substantially full cylindrical form on printing presses taking that kind of plate may be on the order of about three hundred fortyeight thousandth-s of an inch for the inside joined layer. The thickness of the inside joined layer will naturally in any case depend upon the size and particular form of the finished plate required for the particular cylinder and kind of press upon which the plate is to be used, The inside layer of metal, supplied molten, unites molecularly with the prepared surface of the outer sheet, and the whole becomes an integral plate in final contour form to fit on the printing cylinder which is to carry it, and being free from differential stresses. The inner layer supplied molten may vary somewhat in composition, depending upon the metal which has been used for the etched sheet, and is generally of lower melting point, to allow union without jeopardizing the face of the plate, and thus for instance in the case of zinc plates and the like a relatively low melting alloy may be applied. Desirably, the alloy may contain at least a small per cent of tin. Type metal, babbitt, etc. may be employed.

The preparing or fluxing of the surface of the facing sheet, as above mentioned, is such as to be appropriate to the particular metals being joined, and, for example, in the case of zinc sheet facing, the back surface of the sheet after suitable cleaning may be treated with hydrochloric acid containing dissolved zinc. Desirably, thin tinfoil is laid on this surface and the sheet may be subjected on a hot plate to a temperature sufiicient to heat and tin the surface. In the subsequent operation of running the molten inner metal against this prepared surface, the temperature of the molten metal, as above indicated will be consistently lower than the melting point of the outside facing sheet, but for example should be not lower than about 575 F., and desirably around 590 F. where applying a molten alloy of lead withvantimony and usually tin. The molten inner layer of alloy joins to the facing sheet, and after solidifying, the composite plate is finished by trimming the edges of the zinc or facing plate, trimming the ends as may be necessary, and usually beveling, and bringing the interior if necessary to precise diameter dimension, and routing out non-printing areas if desired. Such routing may be carried out to any desired extent with the construction here involved, and may involve not only the facing, but the metal of the inner layer also. The plate thus prepared is mounted on the cylinder of the press, as usual, and is ready for the printing operation. In the claims, where it is stated that the plate is positioned against an outer cylindrical supporting surface it will be understood that .this is intended to include any proper arcuate surface when the sheet is not to form a complete cylinder.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. An etched printing plate, comprising a substantially cylindrical zinc layer etched to form a desired printing surface, and a molecularly united thicker tin-containing back portion free from differential bending stress, non-printing areas of the printing surface being routed out.

2. An etched printing plate, which comprises an arcuate sheet zinc layer etched to form a desired printing surface, and a molecularly united thicker back portion of lower melting metal free from differential bending stress, non-printing areas of the printing surface being routed out.

3. An etched printing plate, which comprises a curved thin metal surface portion etched to form a desired printing surface, and a molecu-' larly united thicker metal back portion of lower melting point free from differential bending stress.

4. An etched printing plate, comprising an etched curved metal printing surface portion, and a molecularly unlted back portion of metal of lower melting point free from differential bending stress.

SAMUEL B. ANSON. 

